One-step beyond: northernmost record of Berghia verrucicornis (Costa, 1867)

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Gabin Droual, Guillaume Bridier

To cite this version:

Gabin Droual, Guillaume Bridier. One-step beyond: northernmost record of Berghia verrucicornis

(Costa, 1867). An Aod - Les cahiers naturalistes de l’Observatoire marin, Vincent Le Garrec, Jacques

Grall, 2020. �hal-02986674�

One-step beyond: northernmost record of

Berghia verrucicornis

(Costa, 1867)

Gabin Droual

_{& Guillaume Bridier}

1_{IFREMER, ODE, DYNECO, LEBCO, F-29280 Plouzané, France} 2_{IFREMER, RBE, EMH, F-44000 Nantes, France} 3_{Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzané, France}

Abstract

The nudibranch Berghia verrucicornis (Costa, 1867) was sampled during a citizen science survey along the Brittany coast as part of a macrofaunal species monitoring in the intertidal area. This note reports for the first time the occur-rence of B. verrucicornis in Brittany. In addition, it is also the northernmost record for this species. Its distributional range is thereby increased by 200 km to the north.

Keywords: Berghia verrucicornis; Brittany; citizen science; new record; nudibranch

Un pas en avant : signalement septentrional de l’espèce Berghia verrucicornis (Costa, 1867)

Résumé

Le nudibranche Berghia verrucicornis (Costa, 1867) a été échantillonné lors d’une sortie de science participative le long des côtes bretonnes, dans le cadre d’un suivi de la macrofaune des estrans. Cette note rapporte pour la première fois l’occurrence de B. verrucicornis en Bretagne. De plus, il s’agit du signalement le plus septentrional pour cette espèce. Son aire de distribution s’agrandit de 200 km vers le nord.

Mots-clés : Berghia verrucicornis ; Bretagne ; nouveau signalement ; nudi-branche ; science participative

Corresponding author:

Gabin Droual (e-mail:|gabin.droual|@|ifremer.fr|)

Reçu le 23 mars 2020 ; accepté après révision le 31 juillet 2020 ; en ligne le 12 août 2020. Received 23rd March 2020; accepted in revised form 31st July 2020; online 12th August 2020.

of the intertidal modifications”) citizen science program was created in 2018 by Bretagne Vivante - SEPNB, an association aiming to protect the nature in Brittany. OBCE monitors several marine species whose distributional ranges reach their northern or southern limit on the coasts of Brittany. Gathering all marine enthusiasts naturalists and some scientists experts of Brittany, the project also aims to record any taxa which might newly occur either naturally or as introduced by humans activities within the area (Hily, 2018).

Recently, several sea slugs species have been reported either for the first time in Brittany, such as for the small species Trinchesia genovae (O’Donoghue, 1926), either as a northern-most record for Spurilla neapolitana (Delle Chiaje, 1841) or for both reasons like Babakina anadoni(Ortea, 1979) and Felimida krohni (Vérany, 1846) (Delemarre et al., 2016;Droual, 2018;Grall et al., 2015). Unfortunately, the naturalist knowledge is currently decreasing in research laboratories as well as funding allocated for biodiversity assessment. In such context, citizen science might appears as a useful tool to help the scientists to cope with the lack of time and knowledge. Combined with the technology (e.g. passionate groups on social media), citizen marine naturalists might then act as early detectors of non-indigenous species or new distributional records (Giovos et al., 2019;Kleitou et al., 2019). In this study, we present such an example: Berghia verrucicornis is recorded in Brittany for the first time, a record which correspond to its northernmost record, during an OBCE field survey.

Methods

Macrofaunal biodiversity assessment were made without strict protocol. The specimen was sampled under a rock boulder close to the kelps level at the mean low water level the 20th February 2019 at ‘La Pointe du Diable’, Plouzané, France (48°2101700N 4°33029,500W) (Fig-ure 1). The alive specimen was examined under a Zeiss Stemi 2000-C stereomicroscope and photographed with a Canon EOS 600D mounted on stereomicroscope. After identification, the specimen was fixed in 96 % alcohol, freshened up three times and kept at ambient temper-ature.

The specimen is available at the Paris National Museum of Natural History under the collection number MNHN-IM-2013-86089.

Results

Material examined: one specimen, maximal length around 20 mm (specimen stretched out), Pointe du Diable, Plouzané, Brittany, France, the 20th February 2019.

Identification

The species level have been reached thanks to all recent diagnosis available through the liter-ature (Ballesteros et al., 2012;Calado & Silva, 2012;Carmona et al., 2014;García-Gómez et al.,2011).

Figure 1: Map showing the northern historical sighting site (black square) of Berghia verrucicornis (Costa, 1867) at Le Croisic made byLabbé(1931) and the current northern record (black circle) at La Pointe du Diable close to Brest city.

Diagnostic criteria (Figure 2)

Papillate rhinophores short and orange with white tips; two obvious orange bands from the rhinophores to the oral tentacules; two eyes clearly visible. Behind eyes, fade orange triangle linked to the pericardic region. Orange spot on pericardic area; orange line continuing to the cerata group 4. Cerata with white tip; subapical bright orange ring.

Discussion

Berghia verrucicornisdistribution, before the record here reported, ranges from the Mediter-ranean Sea to the Atlantic. In the Eastern Atlantic, it lives from Le Croisic (Labbé, 1931) in France to the African coasts (Edmunds, 1968;Muniain & Ortea, 1999). The northern limit of B. verrucicornis now reaches the Iroise Sea at the entrance of the Bay of Brest. Such localization expands the former northernmost locality by some 200 km to the north (Figure 1). Among the numerous abiotic parameters impacted by climate changes, seawater tempera-tures experience strong increase over the last decades, especially in the European seas (Belkin, 2009). Modification of the seawater isotherms is usually considered as the main driver caus-ing shifts of distributional ranges and reschedulcaus-ing phenology at large spatio-temporal scales (Burrows et al., 2014). Species are expected to adjust their geographical distribution to face these forthcoming environmental changes (Burrows et al., 2014;Stuart-Smith et al., 2017).

Figure 2: Berghia verrucicornis (Costa, 1867), alive specimen from ‘La pointe du Diable’, Plouzané near Brest, 20th February 2019, MNHN-IM-2013-86089. Scale bar: 5 mm.

Some studies demonstrate that marine species will track the isotherms velocities mainly pole-ward even if some species might go further south or show no responses, depending on their physiology, dispersal abilities, population size, but also from physical barriers, habitat or food suitability (Burrows et al., 2014;Pinsky et al., 2013). According to a meta-analysis, benthic Mollusca (post-larval stages for gastropods, bivalves, chitons) leading edge is increasing by almost 20 km per decade (Poloczanska et al., 2013). The extension of Berghia verrucicornis is here reported 200 km from its last northern historical record almost 10 decades ago (Labbé, 1931) which seems coherent with the results ofPoloczanska et al. (2013). However, because the temperature started to increase noticeably later than the last report of B. verrucicornis, the species might have expand recently its distributional range at a rate higher than 20 km per decade (Belkin, 2009;Cheng et al., 2019). The expansion of the geographical distribu-tion of Berghia verrucicornis probably results from the effect of climate change on seawater isotherms distribution rather than from a local introduction.

It also has to be noticed that new records of small nudibranch species along Brittany coast are not surprising, as this taxon has received poor attention during the last decades in this area. Indeed, the last large focused scientific study on nudibranchs in Brittany was

published more than 40 years ago (Bouchet & Moreteau, 1975) and has never been updated since. During most of benthic monitoring projects, the identification of nudibranchs usually does not reach the species level since the organisms lose their colours and cerata and are often in bad condition when stored in formalin (Droual, 2018). Additionally, as discussed above, climate change induce locally new distributional ranges for some taxa and lead to the establishment of new allochthone nudibranch species. This group should thus receive specific attention during campaigns or biodiversity assessment fieldworks, especially on live material, to acquire more data and to update species checklists (work in progress). Range shifts induced by climate change are usually easier to observe on the intertidal zone compared to the deeper waters, thereby programs like the OBCE project may be essential tools to improve biodiversity monitoring at large scales and in areas under-monitored by scientists (Garcia-Soto et al., 2017;

Wethey & Woodin, 2008).

Acknowledgements

The authors thank, Christian Hily for his implication in the OBCE project to motivate citizen naturalists to better known the marine environment and promote the naturalist knowledge in our society. The authors also acknowledge Céline Cordier for the map production.

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